The present invention relates to a novel indolocarbazole derivative or a pharmaceutically acceptable salt thereof. These compounds are expected to be useful as a therapeutic agent for thrombocytopenia.
The decrease in the number of blood platelets due to various kinds of hematopoietic disorders causes grave symptoms including an increased tendency to hemorrhage. At present, platelet transfusion is effective against such decreases. However, a sufficient amount of blood platelets is not always supplied. In addition to platelet transfusion, interleukin (IL) 6 and IL 11, which are hematopoietic factors that stimulate the production of blood platelets are known [Blood, 75, 1602 (1990); Blood, 81, 901 (1993)].
Indolocarbazole derivatives having staurosporine skeleton are known to have protein kinase C inhibitory activity, anti-tumor activity and antibacterial activity [WO89/07105, WO92/17181, Japanese Published Unexamined Patent Application No. 220196/87, Japanese Published Unexamined Patent Application No. 86068/93], platelet aggregation inhibitory activity [Japanese Published Unexamined Patent Application No. 72485/91, Japanese Published Unexamined Patent Application No. 163325/91, Japanese Published Unexamined Patent Application No. 220194/91, Japanese Published Unexamined Patent Application No. 145085/92, Japanese Published Unexamined Patent Application No. 364186/92], vasodilating activity [Japanese Published Unexamined Patent Application No. 143877/89, Japanese Published Unexamined Patent Application No. 9819/90], antiobestic activity [WO89/11295] or macrophage activating activity [Journal of Antibiotics, 42, 1619 (1989)] and so on.
However, it is not known that indolocarbazole derivatives have an activity to stimulate the production of blood platelets.
Most of the known indolocarbazole derivatives have hydrogen at the position corresponding to R.sup.1 in the following formula (I). Alternatively, the known indolocarbazole derivatives have lower alkyl at the position corresponding to R.sup.1, and hydrogen at the positions corresponding to R.sup.3 and R.sup.4 in the following formula (I).